1. Field of the Invention
The present invention relates to a microactuator control apparatus using shape memory alloy (SMA) elements activated by the application of thermal energy, either from a high temperature gas or an optical source.
2. Description of the Related Art
Shape memory alloys, such as the well-known nickel-titanium type, exhibit novel properties, in which they exhibit the ability to return to a predetermined shape when heated. When a SMA is cold, or below its transformation temperature, it exhibits very low yield strength and can be deformed quite easily into any desired shape which it will retain. However, when heated above its transformation temperature it will undergo a change in crystal structure which causes it to return to its original shape. In the event the SMA encounters any resistance during this transformation, it can exert extremely large forces upon the resisting media.
Thus SMA materials have proven to be invaluable for remote actuation devices. Although many uses of SMA materials have been heretofore disclosed as actuator devices these prior art devices generally employ electrical energy as their means for activating the SMA elements. For example see U.S. Pat. Nos. 5,769,389; 5,410,290; 5,271,075; 5,024,497; 5,004,318; and 4,987,314. However, using the SMA material itself to produce resistance heating is not desirable as SMA materials exhibit low electrical resistance thereby requiring higher current flow than other more suitable resistance heating elements.
The present invention teaches a SMA microactuator device useful for the operation of a servo valve in an aircraft control system and/or any other suitable aerospace or non-aerospace application. The present SMA actuator, as disclosed herein, is unique in that it may employ the use of thermal energy from either a hot gas source or from an optical power source to activate the SMA elements. In the hot gas embodiment the flow of hot gas, to the SMA elements, is preferably controlled by optically operated switches or gates. In the optical energy embodiment optical energy, such as laser energy, may be applied directly to the SMA elements using known optical energy transmission means. Thus it is unnecessary to provide a source of electrical energy for operation of the microactuator. The hot gas and/or optically operated SMA actuators, as taught herein, are particularly suitable for use on gas turbine powered aircraft where a ready and abundant supply of high temperature gas is available from the compressor and/or turbine section of the gas turbine engine. However, one skilled in the art may find other suitable applications for SMA actuators as taught herein.